This invention relates to heating efficiency and, more particularly, to a system for increasing furnace efficiency.
The recent public concern over fuel consumption in this country and throughout the world has emphasized the importance of energy efficient appliances. One particular device which uses substantial energy is the ordinary furnace for home or business. The commonly used oil and gas fired forced air furnaces consume substantial quantities of natural resources in short supply.
Furnace efficiency, however, is affected by external factors as well as its internal construction. Most forced air furnaces use air from the surrounding room for combustion. This promotes a draft within the building because air from elsewhere within the building moves to replace the air used in combustion. Also, cold air from outside the building is drawn through the cracks in the building and through the window and door frames to further create drafts. The end result is a decrease in the heating efficiency of the furnace and an increase in fuel consumption.
One solution to this problem is to supply outside air, rather than room air, directly into the furnace for combustion, as suggested in the following U.S. Pat. Nos. 4,038,963; 3,805,764; 3,906,925; 2,711,683; 2,764,972. However, previous efforts to supply outside air for combustion have not proven satisfactory because the amount of cold outside air entering the furnace has not been adequately controlled.
A further problem contributing to furnace inefficiency is the unnecessary loss of heat through the chimney flue or exhaust. When the furnace is shut off, residual heat promotes convection currents which cause warm air drawn from the furnace room to leave through the chimney. A manually operated damper located in the flue has proven cumbersome, impractical and undependable because it must be opened or shut each time the furnace operates or shuts off. U.S. Pat. No. 3,906,925 has suggested a motor driven damper activated by the furnace thermostat, but this unnecessarily complicated system apparently depends on the special damper motor and lacks a back-up method of operating the damper. Thus, it is subject to the danger of a heat build-up due to a closed damper and an operating furnace in the event of a malfunction.